Just as air components (primarily nitrogen, oxygen, and carbon dioxide) are included in addition to the flammable gas methane that is included in coal mine gas obtained from a coal mine, for example, flammable gases that exist in nature are often obtained as a raw gas that includes air components in addition to the flammable gas. In order to effectively utilize such a raw gas as a fuel, the air components included in the raw gas must be removed, and the flammable gas included in the raw gas must be concentrated.
An adsorption-type concentration device that uses an adsorbent composed of natural zeolite to selectively adsorb air components in relation to methane is known as a concentration device for removing air components from the coal mine gas and concentrating the methane (see Patent Document 1, for example).
The adsorption-type concentration device disclosed in Patent Document 1 is provided with an adsorption tower filled with an adsorbent for selectively adsorbing air components other than a flammable gas, and is configured so as to alternately execute adsorption processing for injecting coal mine gas or another raw gas at a relatively high pressure into the adsorption tower and causing the air components included in the coal mine gas to be selectively adsorbed to the adsorbent; and desorption processing for reducing the pressure inside the adsorption tower below atmospheric pressure and driving out concentrated gas that includes a large amount of the flammable gas that was not adsorbed to the adsorbent or was selectively desorbed from the adsorbent.
[Patent Document 1] Japanese Laid-open Patent Application No. 58-198591